Compressed gas is transported and used in elongated cylinders which are capable of retaining the high pressure of the gas and which meet all regulatory requirements for safety during storage, transport and use. It is critical that these cylinders be able to contain pressure in all directions, including both axial loads (force components parallel to the cylinder axis) and hoop loads (radially directed tome components). For operations where large volumes of compressed gas or a continuous supply is required, cylinders are used which generally measure about 20-40 feet in length and about 1-2 feet in diameter. To contain loads in cylinders of this size, a particularly strong construction is needed. As a result, a common material of construction is high-strength steel. Banks of eight to twelve of these cylinders are usually mounted to truck trailers for transport to sites of usage.
Because of the high density of steel, these cylinders are not readily removable from the trailers by the type of equipment available at the typical site of use. The cylinders are therefore mounted permanently to the trailers. Unfortunately, this requires that the trailer remain at the site of use for the full time that the cylinders are needed. This gives rise to ongoing expenses associated with the trailer itself, such as excise taxes, licensing fees, and costs arising from operational maintenance. Also, while the trailer is at the site of use, it is not available for transporting other cylinders or gases, and the cost of the value of this lost time is frequently borne by the site. Finally, the permanent mounting of the cylinders to the trailer limits the trailer to a single type of compressed gas, requiring different trailers for different gases and different numbers of cylinders.